1. Field of the Invention
The present invention relates to a call connection method for a mobile communication system, and more particularly to a paging method for a mobile communication system.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating the construction of a general mobile communication system. A mobile communication terminal 100 makes a call connection with another mobile communication terminal through another base transceiver subsystem (BTS) 102, a control station 104 for managing the respective base transceiver subsystems, and a mobile switching center 106. Also, the mobile switching center 106 is connected to a home location register (HLR) 108 for storing location information of the respective mobile communication terminals and an authentication center 110 for performing an authentication process.
In operation, the mobile communication terminal 100 searches for the strongest signal transmitted from an adjacent base transceiver subsystem 102 and connects with the corresponding base transceiver subsystem. In this state, if a subscriber dials a phone number to originate a call, a mobile identification number (MIN) and an electronic serial number (ESN) are transmitted together with the phone number. The mobile switching center 106 performs the subscriber's authentication process through the authentication center 110, the base transceiver subsystem 102 transmits a channel allocation message to the mobile communication terminal 100, and the mobile communication terminal 100 starts the call using the allocated channel.
For this call connection, the mobile switching center 106 makes the base transceiver subsystem 102 transmit a paging signal. The mobile communication terminal 100 continuously scans the paging of the base transceiver subsystem 102, and if it detects the paging of its own number, it sends the ESN and the MIN to the nearest base transceiver subsystem 102.
Generally, before the paging starts, the mobile communication terminal 100 selects a proper serving cell, time/frequency-synchronizes with the selected serving cell, and receives related system information.
Also, the mobile communication terminal 100 registers in HLR 108 information on which base transceiver subsystem 102 or control station 104 provides a service to the mobile communication terminal 100. Accordingly, the synchronization and the location registration processes are completed before the paging starts.
That is, the mobile communication terminal 100, after it connects with a certain base transceiver subsystem 102, registers itself in the base transceiver subsystem 102 in order to inform that it is located within a receiving area of the corresponding base transceiver subsystem 102. This registered information is written in a database of the network, so that the corresponding base transceiver subsystem 102 can page the mobile communication terminal 100 registered in the corresponding base transceiver subsystem 102 if a communication with the mobile communication terminal 100 such as a call connection is needed.
Here, in order to detect the location and connection state of the mobile communication terminal 100 and to achieve a call connection, the base transceiver subsystem 102 transmits a paging signal, and the mobile communication terminal 100 scans the paging signal from the base transceiver subsystem 102. This process is for searching for the base transceiver subsystem 102 most suitable for the mobile communication terminal 100, and is an essential function for the mobile communication system.
The purpose of the paging is to inform the mobile communication system 100 of a phone call. Generally, the paging is performed by periodically allocating a paging channel (PCH) to the mobile communication terminal 100.
According to a conventional paging method, the channel information for paging is shared by all mobile communication terminals, and is divided, so that the paging of other mobile communication terminals can be performed.
These respective unit blocks are call paging channels (PCHs). At this time, since a specified mobile communication terminal does not know at what time point the paging signal for itself comes, it must read all the related PCHs. This means that the mobile communication terminal must continuously perform a receiving operation in a state in which no connection is actually made, resulting in excessive power consumption. In order to avoid this, a method for classifying all the mobile communication terminals by paging groups has been introduced.
Such paging groups are illustrated in FIG. 2. As shown in FIG. 2, there are paging groups A, B, C, . . . H. The PCH position for one paging group is periodically given as illustrated in FIG. 2.
During paging through the paging groups, the respective mobile communication terminal finds its own paging group through its own inherently provided information that includes a product identification number, and receives only the PCH of the corresponding paging group.
After the paging of one paging group (for example, paging group A), a paging period, which is a time period required for paging the corresponding paging group A, is given. This paging period is determined according to the number of paging groups. That is, if the paging period is large, the number of paging groups increases, while if the paging period is small, the number of paging groups decreases.
Different methods of determining the paging period are used in different mobile communication systems. For example, in case of a global system for mobile communication (GSM) network, the BTS determines the paging period using an internally determined value through system information, and in case of a general packet radio service (GPRS) network, the paging period is determined through a type of negotiation when the mobile communication is registered.
Once the period is determined, the PCH for the corresponding mobile communication terminal is allocated by accurately observing the paging period so that the BTS receives only the corresponding position without any separate engagement and receives the connection request.
The respective mobile communication terminal periodically receives the PCH that belongs to its own paging group, confirms the contents of the PCH, and attempts the connection in response to the PCH only when it is the subject of paging. Otherwise, it ignores the contents of reception.
However, due to the characteristics of a wireless network, the mobile communication terminal may fail to receive a portion of PCH information, and may not know whether it has been paged. In this case, if no response is received, the BTS pages again the same mobile communication terminal, and after the paging is performed as many times as an internally pre-determined number, it recognizes that the corresponding mobile communication terminal is absent. However, if a response is received from the mobile communication terminal during the paging, the BTS performs the call connection.
If the time that the mobile communication terminal responds to the paging from the BTS is defined as a paging response duration (PRD) after the BTS starts the paging of the mobile communication terminal, it can be expressed by “PRD=paging period×number of failures in PCH reception.” Here, the reason why the PRD is not defined with “number of failures in PCH reception-1” is that the time required for initially waiting for the PCH position of the paging group of the mobile communication terminal after the BTS decides to page the corresponding mobile communication terminal may be the maximum 1-paging period.
The failure in PCH reception may mean that the mobile communication terminal receives the corresponding PCH from the BTS but cannot read received information, or information that the mobile communication terminal attempts to send to the BTS is not stably transferred to the BTS.
Specifically, there is no case in which the mobile communication terminal cannot receive the PCH. That is, the mobile communication terminal always receives radio frequency (RF) signals, always at determined time points. However, the mobile communication terminal may fail to decode the received signal. Also, there is no case in which the mobile communication terminal cannot connect to the BTS after receiving the PCH, but information that the mobile communication terminal attempts to send to the BTS may not be stably transferred to the BTS. In other words, the mobile communication terminal and the BTS unconditionally receive information at the engaged time points, but may not read the received information.
As shown in FIG. 2, lengthening or shortening the paging period brings a wide difference in the methods for setting the paging period, performing the paging according to the paging period, and scanning the paging information according to the paging period.
That is, when shortening the paging period, the response speed of the paged mobile communication terminal becomes high, the call connection is promptly performed accordingly, and the PRD value becomes small when the PCH reception for the same number of times fails. In this case, however, due to the mobile communication terminal's scanning operation of the paging, the battery consumption increases, and the number of mobile communication terminals that can be accommodated in the same PCH decreases.
If many mobile communication terminals are used in a state in which the number of mobile communication terminals that can be accommodated in the same PCH decreases, the number of mobile communication terminals allocated in the same paging group increases due to the small number of paging groups, and this causes the number of mobile communication terminals that cannot be timely allocated with the PCH to increase and also causes the time required for the initial paging to be lengthened. Consequently, in order to shorten the paging period, many PCHs must be secured in proportion to the expected number of mobile communication terminals.
Meanwhile, when lengthening the paging period, in contrast with the case of shortening the paging period, since the scanning period required for the mobile communication terminal's scanning operation of the paging is shortened, the battery consumption decreases, and the number of mobile communication terminals that can be accommodated in the same PCH increases. However, the response speed of the paged mobile communication terminal is low, the call connection becomes slow, and the PRD value becomes large when the PCH reception for the same number of times fails.
Accordingly, there is a need for a new paging method for gaining both advantages obtained by shortening and lengthening the paging period rather than fixing the paging period.